The present disclosure relates to subterranean operations and, more particularly, to systems and methods for managed pressure operations and testing in subterranean well bores.
In constructing a subterranean well for production of hydrocarbons, once a well bore has been drilled into the subterranean formation of interest, a pipe string (e.g., casing, liners, expandable tubulars, etc.) is often run into the well bore and cemented in place. The process of cementing the pipe string in place is commonly referred to as primary cementing. In a typical primary cementing method, a cement composition may be pumped into an annulus between the walls of the well bore and the exterior surface of the pipe siring disposed therein. The cement composition may set in the annular space, thereby forming an annular sheath of hardened, substantially impermeable cement (e.g., a cement sheath). This cement sheath may support and position the pipe string in the well bore, bond the exterior surface of the pipe string to the subterranean formation, prevent communication and migration of fluids between producing zones, aquifers (and any contamination related thereto), and/or protect the pipe string from corrosion. Remedial cementing methods also may be used, for example, to seal cracks or holes in pipe strings or cement sheaths, to seal highly permeable formation zones or fractures, to place a cement plug, and the like.
It is often desirable or required to verify the integrity of the cement and/or the wellhead seal assembly at the wellbore before hydrocarbon production from that well begins. Positive pressure testing and negative pressure testing (e.g., inflow testing) are two types of testing that are sometimes used to provide this verification. A positive pressure test may be used to check the integrity of the well by testing whether the casing and wellhead seal assembly can contain higher pressure than surrounds them. In a positive pressure test, additional fluid is pumped into the well below any blow-out preventer, the pumps are shut off, and the pressure in the well is monitored. A constant pressure with the pumps shut off typically indicates that the casing, wellhead seal assembly, and blow-out preventer are containing internal pressure and are not leaking. Conversely, in a negative pressure test, the pressure in the well bore is reduced to a level lower than the pressure in the formation (e.g., by pumping heavier fluid out of the well and replacing it with a lighter fluid), and then pressure in the well is monitored with the pumps shut off. A constant pressure in the negative pressure test indicates that the cement in the well can contain fluids in the formation and prevent them from leaking into the well.
Well bores penetrating subterranean zones that contain oil, gas, and/or other fluids typically experience an influx of those fluids into the well bore if the formation fluid pressure is greater than the well bore pressure. Managed pressure techniques are sometimes employed in drilling and cementing of subterranean well bores in order to control the bottom hole pressure in the well bore at the surface (e.g., to maintain pressure above the pore pressure of the formation), and thus control the influx of formation fluids into the well bore during those operations. Unlike conventional techniques that rely on the density of fluids circulated in the well bore to maintain pressure in the well, managed pressure techniques involve the use of backpressure and maintaining the well bore in a closed pressure loop in order to maintain the desired pressure in the well bore. Most systems for managed pressure drilling include a rotating control device, blowout preventer, and a subsystem of chokes, valves, flow lines, pumps, and other equipment installed at the well site to control the pressure in the well bore and flow of fluids into and out of the well bore.
While embodiments of this disclosure have been depicted and described and are defined by reference to example embodiments of the disclosure, such references do not imply a limitation on the disclosure, and no such limitation is to be inferred. The subject matter disclosed is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those skilled in the pertinent art and having the benefit of this disclosure. The depicted and described embodiments of this disclosure are examples only, and not exhaustive of the scope of the disclosure.